Contactless Radiofrequency Identification Devices (RFIDs) are increasingly used for identification of persons moving about in controlled access zones or transiting from one zone to another. As a result, the market for identity document type secure documents such as passports, identity cards or others is booming. A contactless RFID is a device made up of an antenna and a chip connected to the terminals of the antenna. The chip is usually not powered by batteries and receives its energy by an electromagnetic coupling between the antenna of the reader and the antenna of the RFID, information is exchanged between the RFID and the reader and particularly information stored in the chip that relates to the identification of the holder of the object on which the RFID is located and to his/her authorization to enter into a controlled access zone.
In this manner, passports can incorporate RFIDs to identify the passport holder. The chip memory contains information such as the identity of the passport holder, his/her country of origin, his/her nationality, visas of different countries visited, dates of entry, restrictions of movements, biometric elements, etc. In order to include the RFID in the passport, there exist several solutions that consist in either directly printing the antenna on the cover board of the passport and connecting the chip to it or using an external element known as “inlay” carrying the RFID. Whatever the solution, the RFID is incorporated either in the bottom cover board of the passport or in the top cover board. In the case of an identity card, the antenna is screen printed directly on one of the layers which make up the card and the chip is connected to it.
Access to data of the chip is made by remote electromagnetic coupling with a reader also equipped with an antenna. When the antenna of the reader is powered, an electric current flows through it, which generates an electromagnetic flow. In order to be read, the identity booklet is placed on the reader at a location designed for this purpose. Once the booklet is in place, the antenna of the booklet is crossed by electromagnetic field lines emitted by the reader and the antenna thus tuned to the same frequency band as the reader receives the energy required for its power supply; it can thus communicate with the reader and exchange data. For optimal communication, the antenna of the booklet must be placed parallel to the antenna of the reader and at a distance from the reader that must be less than a minimum distance, so that the energy is sufficient to operate the chip.
The major problem that commonly arises in contactless documents in general, and in secure documents that contain personal information of biometric or civil status type in particular, is the confidentiality of information contained in the radiofrequency device incorporated in the chip of the document. Access to the data contained in the chip must be controllable, particularly when the secure document is not used, so that the confidential data is not retrieved without the knowledge of the document holder.
A solution exists as described in the document WO 2005/066890. The secure document that is described in this document includes a transponder made up of an electronic module connected to an antenna placed on a given surface of a first part of the document, the transponder being designed to communicate by means of remote electromagnetic coupling with a reader, and featuring in addition a passive element for masking the antenna, supported by a second part of the document, which can move with respect to the first part, the masking element being capable of minimizing the coupling between the transponder and the reader to make the reading of the document difficult in a predetermined position of the second part which corresponds to a closed position of the document.
The drawback of such a device resides in the fact that the action on the coupling between the transponder and the reader does not act as an on/off switch but acts so as to attenuate the signal in order to minimize the coupling between the transponder and the reader. Furthermore, since the attenuation of the signal depends on the signal frequency, the greater the attenuation, the higher the signal frequency; the operating frequency of secure documents is 13.56 MHz as defined in the ISO 14443 and 15693 standards. The attenuation of the signal also depends on the characteristics of the masking element such as its thickness and its electrical conductivity, and it also depends on the distance between the passive element and the antenna of the radiofrequency identification device. The closer the masking element is to the antenna, the more efficient it is.
The attenuation level of the signal will thus depend on the manner in which the secure document is held closed. Therefore, a passport placed in a bag and slightly open may be read without the knowledge of its holder. Similarly, a passport whose pages are thick because of wear or the presence of visas will reduce the effectiveness of the passive masking element. The attenuation level of the signal also depends on the thickness of the passport.
In addition, the minimum reading distance between the passport and the reader varies according to the level of the electromagnetic field emitted by the antenna of the reader. The effectiveness of the communication between the reader and the passport thus varies according to the field emitted by the reader. This means that, even when it is equipped with passive masking, the passport can be read with a suitable reader as the passive masking actually reduces the reading distance. This solution therefore does not guarantee the passport holder against untimely reading.